Mapping brain connectome is essential for understanding how the brain works. As the basic unit of neural function, neural circuit serves as the bridge between macroscale structure/function and microscale molecules/signal pathways. However, the structure for many specific functional neural circuits, including the components, connections and distributions, remains to be elucidated. New tracing technology and tracers, especially viral tracers, have contributed to discovery of novel circuits and revealing new features of known canonical circuits.
Viral tracers have been used in neuroscience research. Viral tracers derived from rabies virus (RV) and pseudorabies virus (PRV) have the capacity of tracing neural circuits to retrogradely map the input neural networks [1]. Recombinant vesicular stomatitis virus (VSV) has also been used for anterograde or retrograde transsynaptic circuit tracing [2, 3]. Human herpes simplex virus type 1 (HSV-1) strain H129 (H129) is a potential anterograde transsynaptic neural circuit tracer [4, 5].
However, mapping the details of the output neural circuit anterogradely with high efficiency and resolution remains a challenge. Therefore, there is an imperative need to develop an anterograde tracer with high transsynaptic labelling efficiency.